Catalytic partial oxidation process using a catalyst system having an upstream and a downstream part

ABSTRACT

The invention relates to a process for the catalytic partial oxidation of a hydrocarbonaceous feedstock, wherein a feed mixture comprising the hydrocarbonaceous feedstock and a molecular-oxygen containing gas is contacted with a catalyst system having an upstream part ( 3 ) and a downstream part ( 2 ), the downstream part ( 2 ) being in the form of a porous catalyst bed, wherein the catalyst system is retained in a reactor, the reactor comprising an upstream part ( 5 ) that contains the upstream part ( 3 ) of the catalyst system and a downstream part ( 6 ) that contains the downstream part ( 2 ) of the catalyst system, wherein the upstream part ( 3 ) of the catalyst system only partly fills the cross-sectional area of the fluid flow path of the upstream part of the reactor and the downstream part ( 3 ) of the catalyst system completely fills the cross-sectional area of the fluid flow path of the downstream part of the reactor. The invention further relates to a reactor comprising such a catalyst system and a catalytic reaction zone for the water-gas shift conversion of the effluent of the catalyst system, to a fuel cell system comprising such a reactor and a fuel cell, and to a vehicle provided with such a fuel cell system.

[0001] The present invention relates to a process for the catalyticpartial oxidation of a hydrocarbonaceous feedstock, wherein a feedmixture comprising the hydrocarbonaceous feedstock and amolecular-oxygen containing gas is contacted with a catalyst systemhaving an upstream part and a downstream part, to a reactor comprisingsuch a catalyst system and a catalytic reaction zone for the water-gasshift conversion of the effluent of the catalyst system, to a fuel cellsystem comprising such a reactor and a fuel cell, and to a vehicleprovided with such a fuel cell system.

[0002] Partial oxidation of a hydrocarbonaceous feedstock, in particularhydrocarbons, in the presence of a catalyst is an attractive route forthe preparation of mixtures of carbon monoxide and hydrogen, normallyreferred to as synthesis gas. The partial oxidation of hydrocarbons isan exothermic reaction represented by the equation:

C_(n)H_(2n+2) +n/2O₂ →nCO+(n+1)H₂

[0003] There is literature in abundance on the catalysts and the processconditions for the catalytic partial oxidation of hydrocarbons.Reference is made, for instance, to EP-A-303 438, U.S. Pat. No.5,149,464, EP-B-576 096, WO 99/37380, and WO 99/19249.

[0004] In a catalytic partial oxidation process in a fixed catalyst bed,the temperature of the top layer, i.e. the layer at the upstream end ofthe catalyst bed, is typically higher than the temperature furtherdownstream in the catalyst bed. This is due to the fact that thecatalytic partial oxidation reaction is mass and heat transfer limited,i.e. full conversion is subject to mass and heat transfer limitationsbetween the bulk of the gaseous feed mixture and the catalyst surface,and/or that some endothermic reforming reactions might occur in thedownstream part of the catalyst bed.

[0005] High temperatures in the top layer of the catalyst are unwanted,since the rate of catalyst deactivation increases with temperature.Therefore, there is a need in the art for a catalytic partial oxidationprocess wherein the temperature in the top layer of the catalyst bed canbe reduced.

[0006] In International Patent Application WO 01/46068, it was foundthat, in a process for the catalytic partial oxidation of ahydrocarbonaceous feedstock using a fixed bed catalyst, the temperatureof the upstream part of the catalyst can be reduced by carrying out theprocess in a reactor retaining the fixed bed catalyst, which reactor isdesigned such that a part of the conversion product flows back to thezone just upstream of the catalyst bed.

[0007] It has now been found that, in a catalytic partial oxidationprocess, very high temperatures at the upstream surface of the catalystcan be avoided by using a catalyst system having an upstream partwherein part of the feedstock is converted and a downstream part,wherein the conversion is substantially completed, wherein the upstreampart of the catalyst system only fills part of the cross-sectional areaof the flow path of the feed mixture.

[0008] Accordingly, the present invention relates to a process for thecatalytic partial oxidation of a hydrocarbonaceous feedstock, wherein afeed mixture comprising the hydrocarbonaceous feedstock and amolecular-oxygen containing gas is contacted with a catalyst systemhaving an upstream part and a downstream part, the downstream part beingin the form of a porous catalyst bed, wherein the catalyst system isretained in a reactor, the reactor comprising an upstream part thatcontains the upstream part of the catalyst system and a downstream partthat contains the downstream part of the catalyst system, wherein theupstream part of the catalyst system only partly fills thecross-sectional area of the fluid flow path of the upstream part of thereactor and the downstream part of the catalyst system completely fillsthe cross-sectional area of the fluid flow path of the downstream partof the reactor.

[0009] Reference herein to the cross-sectional area of the fluid flowpath is to the cross-sectional area perpendicular to the overall flowdirection of the fluid. The overall fluid flow direction in the upstreampart of the reactor may be different from the fluid flow direction inthe downstream part of the reactor. Reference herein to completelyfilling the cross-sectional area means that the catalyst bed, i.e. thehoneycomb, foam, wire arrangement, packed bed or the like, completelyfills the cross-sectional area. The catalyst bed as such of thedownstream part of the catalyst system is porous and thus has, bydefinition, open area. This open area is not to be taken into accountfor determining whether the catalyst bed completely fills thecross-sectional area of the fluid flow path.

[0010] Since the cross-sectional area of the fluid flow path in theupstream part of the reactor is only partly filled with catalyst, partof the reactants can pass the catalyst without being contacted with thecatalyst. In the downstream part of the reactor, the fluid flow path iscompletely filled with catalysts and the reactants are forced to contactthe catalyst.

[0011] In the process according to the invention, part of the feedstockis converted at the upstream part of the catalyst system before thepartially converted feedstock is contacted with the downstream part ofthe catalyst system. Preferably 5 to 75% (v/v) of the feedstock isconverted at the upstream part of the catalyst system, more preferably10 to 50% (v/v), even more preferably 15 to 40% (v/v).

[0012] Preferably, the upstream part of the catalyst system is smallerin volume than the downstream part of the catalyst system. Morepreferably, the volume of the upstream part is at most a fifth of thevolume of the downstream part, even more preferably at most a tenth,most preferably at most a twentieth. Reference herein to volume is tothe volume of the catalyst bed or arrangement including its pores.

[0013] As has been described hereinbefore, very high temperatures at theupstream surface of the downstream part of the catalyst system can beavoided in the process according to the invention. Without being boundto any theory, it is believed that the presence of conversion productsin the fluids contacting the downstream part of the catalyst causes areduction of the temperature prevailing at the upstream surface of thedownstream part of the catalyst system.

[0014] Preferably, the temperature of the upstream surface of thedownstream part of the catalyst system is at most 1150° C., morepreferably at most 1100° C.

[0015] It has been found that the temperature of the upstream surface ofthe downstream part of the catalyst system can be further reduced if the(partly converted) feed mixture that contacts the upstream surface ofthe downstream part has a component of its flow direction that isparallel to the upstream surface of the downstream part of the catalystsystem, such as described in International Patent Application WO01/46068. This is for example the case when the feed mixture isapproaching the downstream part of the catalyst in a swirling movement.

[0016] It has been found that, in the process according to theinvention, the temperature at the upstream surface of the downstreampart of the catalyst system is in general lower than the temperature atthe upstream surface of the upstream part of the catalyst system. Itwill be appreciated that it will inter alia depend on the relativevolumes and amounts of catalytic active material of the upstream anddownstream catalyst parts and of the exact configuration of those parts,if and to what extent the temperature at the upstream surface of thedownstream part is lower. The temperature of the upstream surface of thedownstream part of the catalyst system is preferably at least 50° C.lower than the temperature of the upstream part of the catalyst system.

[0017] In order to achieve a high yield in the process according to theinvention, it is important that the degree of feedstock conversion andthe selectivity towards carbon monoxide and hydrogen of the downstreampart of the catalyst system are high. This can be achieved by using adownstream part in the form of a porous catalyst bed, since a porouscatalyst has a relatively high specific surface area. Suitable porouscatalyst beds comprise a porous, fixed arrangement of catalyst carrierprovided with a catalytically active material. Suitable porous, fixedarrangements of catalyst carrier are known in the art. Examples are apacked bed of catalyst carrier particles, a ceramic or metal monolithicstructure such as a foam or a honeycomb, an arrangement of metal gauzesor wires or combinations thereof.

[0018] Since only part of the feedstock needs to be converted at theupstream part of the catalyst system, only part of the feedstock needsto be contacted with the upstream part of the catalyst system. Byarranging the upstream part of the catalyst system in the reactor insuch way that it only partly fills the cross-sectional area of the fluidflow path, part of the feedstock will by-pass the upstream part of thecatalyst, thereby minimising the pressure drop over the upstream part ofthe catalyst system.

[0019] Another consequence of the fact that only part of the feedstockneeds to be converted at the upstream part of the catalyst system isthat the upstream part does not need to have a relatively high specificsurface. Therefore, the upstream part of the catalyst may be in the formof a non-porous fixed arrangement. Suitably, the upstream part of thecatalyst system is in the form of a porous or non-porous fixedarrangement of catalyst carrier provided with catalytically activematerial.

[0020] Since the upstream part of a catalyst is the part that will bemost subjected to thermal shocks, the catalyst carrier of the upstreampart of the catalyst is preferably made of metal.

[0021] Preferably, such a metal catalyst carrier is in the form of anon-porous metal structure, for example a metal foil or plate. Typicallysuch metal foils or plates will have a thickness in the range of from0.1 to 2 mm. A non-porous metal structure can be made of more robustmaterial, i.e. more resistant to high temperatures and high thermalshocks, than porous metal arrangements such as foams or arrangements ofmetal wires. Thus, by using a non-porous metal structure as the catalystcarrier of the upstream part of the catalyst system, the catalyst systemis most robust at the point where the conditions, especially temperatureand thermal shocks, are most severe.

[0022] Reference herein to conversion is to the percentage of thehydrocarbonaceous feedstock that is converted into lowerhydrocarbonaceous compounds and/or carbon oxides. Reference herein toselectivity is to the sum of moles carbon monoxide and hydrogen produceddivided by the theoretical maximum sum of moles carbon monoxide andhydrogen that can be produced. Reference herein to a porous catalyst isto a catalyst having pores, i.e. spaces or interstices between adjacentportions of the catalyst, having an average diameter in the order ofmagnitude of 0.05 to about 3 mm. These pores are to be contrasted withpores which may be present in the catalyst material itself, typicallyhaving an average diameter in the order of magnitude of tenths to a fewmicrometers. Examples of porous structures are foams, honeycombs, wirearrangements and packed beds of particles.

[0023] Suitable catalyst carrier materials, both for the upstream andthe downstream part of the catalyst system, are well known in the artand include refractory oxides, such as silica, alumina, titania,zirconia and mixtures thereof, and metals. Preferred refractory oxidesare zirconia-based, more preferably comprising at least 70% by weightzirconia, for example selected from known forms of (partially)stabilised zirconia or substantially pure zirconia. Most preferredzirconia-based materials comprise zirconia stabilised orpartially-stabilised by one or more oxides of Mg, Ca, Al, Y, La or Ce.Preferred metals are alloys, more preferably alloys containing iron,chromium and aluminium, such as fecralloy-type materials.

[0024] Metal catalyst carriers are preferably coated with a stabilisedor partially stabilised zirconia. The zirconia layer is coated on thecatalyst carrier prior to applying the catalytically active metal(s) onit. Advantages of such a coating are that the stability and the yield ofthe catalyst are improved and that direct contact between thecatalytically active material and the metals from the metal carrier isminimised or avoided.

[0025] The stabilised or partially stabilised zirconia may be coated onthe catalyst carrier by techniques known in the art, preferably by meansof washcoating techniques such as spraying, dipping or directapplication of a sol or suspension of zirconia. Preferably, the carrieris dried and calcined after washcoating. The sol or suspension ofzirconia may comprise small amount of other oxides or binders, forexample alumina. Preferably, the amount of other oxides or binders isless than 20% by weight, based on the amount of stabilised zirconia,more preferably less than 10% by weight.

[0026] Preferably, the zirconia is stabilised with one or more oxidesselected from oxides of Ca, Mg, Al, Ce, La, and Y, more preferablyselected from Ca and Y. Preferably, the amount of stabiliser is in therange of from 1 to 10% by weight, based on the weight of stabilisedzirconia, preferably in the range of from 3 to 7% by weight.

[0027] Both the catalyst carrier of the downstream and of the upstreampart of the catalyst system is provided with a catalytically activematerial, preferably a catalytically active material suitable for thepartial oxidation of hydrocarbonaceous feedstocks. Such catalyticallyactive materials are known in the art. One or more metals selected fromGroup VIII of the Periodic Table of the Elements are very suitable ascatalytically active material. Rhodium, iridium, palladium and/orplatinum are preferred, especially rhodium and/or iridium. Typically,the catalyst comprises the catalytically active metal(s) in aconcentration in the range of from 0.02 to 10% by weight, based on thetotal weight of the catalyst, preferably in the range of from 0.1 to 5%by weight. The catalyst may further comprise a performance-enhancinginorganic metal cation selected from Al, Mg, Zr, Ti, La, Hf, Si, Ba, andCe which is present in intimate association supported on or with thecatalytically active metal, preferably a zirconium cation.

[0028] The catalyst carrier is provided with the catalytically activematerial by means known in the art, e.g. by impregnation or(co)precipitation.

[0029] The process according to the present invention is particularlyadvantageous if the catalyst bed of the downstream part of the catalystsystem comprises a fixed arrangement of a metal catalyst carrier. Porousmetal arrangements of such as metal foams, honeycombs or arrangements ofmetal gauze, wire or foil, are very suitable catalyst carriers forcatalytic partial oxidation processes, because they are very resistantto thermal shocks. A disadvantage of metal arrangements, especially ifthey contain thin metal wires, however, is that the metal can melt if itis exposed at high temperatures. It will be appreciated that the meltingtemperature depends inter alia of the metal composition, the form of themetal arrangement and the duration of the exposure to that temperature.In the process according to the present invention, very hightemperatures at the upstream surface of the downstream part of thecatalyst system are avoided such that wire arrangements of metals can beused under severe process conditions as catalyst carrier for thedownstream part.

[0030] An advantage of a metal catalyst carrier in the upstream part ofthe catalyst system is that it may be provided with means forelectrically heating it, in order to facilitate catalytic ignition ofthe upstream part of the catalyst during start-up of the catalystsystem. The metal catalyst carrier of the upstream part may for examplebe provided with an electrical igniter. Alternatively, the metalupstream part may be in the form of an igniter. This may for example berealised by using a narrow strip of metal as the catalyst carrier of theupstream part of the catalyst system, over which a potential differencecan be applied.

[0031] In the catalyst system of the process of the present invention,the catalytic composition of the upstream part and of the downstreampart can be optimised independently from each other. The composition ofthe upstream part will be optimised towards resistance to hightemperatures and thermal shock, whereas the composition of thedownstream part will be optimised towards maximum degree of conversionand selectivity.

[0032] Preferably, the distance between the upstream part and thedownstream part of the catalyst system is small, such that heat lossesare minimised, i.e. that a maximum of the heat contained in the effluentfrom the upstream part of the catalyst system is maintained in thereaction zone. A greater distance between the upstream and thedownstream parts of the catalyst system requires a better insulation ofthe reactor against radiative heat losses. The upstream part of thecatalyst system may be arranged on part of the upstream surface of thedownstream part of the catalyst system, provided that the feed mixtureand the feedstock converted at the upstream part can pass the structurein order to contact the downstream part.

[0033] The upstream part of the catalyst system may be provided withmeans for determining its temperature, e.g. a resistive temperaturesensor in the form of a Pt wire. There is a direct dependency of thetemperature of the upstream part of the catalyst and the carbon/oxygenratio in the feed mixture of catalytic partial oxidation reactions.Thus, such an upstream catalyst with temperature sensor can beadvantageously used to control the carbon/oxygen ratio in the feedmixture.

[0034] Suitable hydrocarbonaceous feedstocks for the process accordingto the invention comprise hydrocarbons, oxygenates or mixtures thereof.Oxygenates are defined as molecules containing apart from carbon andhydrogen atoms at least 1 oxygen atom which is linked to either one ortwo carbon atoms or to a carbon atom and a hydrogen atom. Examples ofsuitable oxygenates are methanol, ethanol, dimethyl ether and the like.The hydrocarbonaceous feedstock is gaseous when contacting the catalyst,but may be liquid under standard temperature and pressure (STP)conditions, i.e. at 0° C. and 1 atmosphere. Preferred hydrocarbonaceousfeedstocks are hydrocarbons. The process according to the presentinvention is especially advantageous if the feedstock is a hydrocarbonstream having an average carbon number of at least 2. Preferably, thefeedstock is a hydrocarbon stream having an average carbon number of atleast 6.

[0035] The oxygen-containing gas may be oxygen, air, or oxygen-enrichedair, preferably air.

[0036] The hydrocarbonaceous feedstock and the oxygen-containing gas arepreferably present in the feed mixture in such amounts as to give anoxygen-to-carbon ratio in the range of from 0.3 to 0.8, more preferablyin the range of from 0.35 to 0.65, even more preferably in the range offrom 0.40 to 0.60. References herein to the oxygen-to-carbon ratio referto the ratio of oxygen in the form of molecules (O₂) to carbon atomspresent in the hydrocarbonaceous feedstock. If oxygenate feedstocks areused, e.g. ethanol, oxygen-to-carbon ratios below 0.3 can suitably beused.

[0037] Preferably, the feed mixture additionally comprises steam. Ifsteam is present, the steam-to-carbon ratio is preferably in the rangeof from above 0.0 to 3.0, more preferably of from above 0.0 to 1.5, evenmore preferably of from above 0.0 to 1.0.

[0038] The feed mixture may be contacted with the catalyst at anysuitable gas hourly space velocity (GHSV). In the process according tothe invention, the GHSV will be typically in the range of from 20,000 to10,000,000 Nl/l/h (normal litres of gaseous feed mixture per litre ofcatalyst per hour), preferably in the range of from 100,000 to2,000,000, Nl/l/h, more preferably in the range of from 200,000 to1,000,000 Nl/l/h. Reference herein to normal litres is to litres at STP(0° C. and 1 atm.).

[0039] The feed mixture may be contacted with the catalyst system at apressure up to 100 bar (absolute), preferably in the range of from 1 to50 bar (absolute), more preferably of from 1 to 10 bar (absolute).

[0040] The process of this invention could very suitably be used toprovide the hydrogen feed for a fuel cell. The conversion of fuel intohydrogen that is suitable for use in a fuel cell is generally carriedout is a so-called fuel processor, comprising a first reaction zone forpartially oxidising and/or reforming a fuel and a second reaction zonefor the water-gas shift conversion of the effluent of the first reactionzone, optionally followed by a reaction zone for the removal of carbonmonoxide from the effluent of the second reaction zone.

[0041] Accordingly, the present invention further relates to a reactorcomprising the catalyst system as hereinbefore defined, the reactorfurther comprising a catalytic reaction zone for the water-gas shiftconversion of the effluent of the downstream part of the catalystsystem.

[0042] The reactor according to the invention may optionally comprise areaction zone for the removal of the remaining carbon monoxide from theeffluent of the catalytic reaction zone for the water-gas shiftconversion, preferably a catalytic reaction zone for the selectiveoxidation of carbon monoxide.

[0043] According to a further aspect, the present invention relates to afuel cell system comprising the reactor as hereinbefore defined and afuel cell. The fuel call may for example be a PEM fuel cell or a solidoxide fuel cell. Such a fuel cell system can for example be applied indomestic system for generating heat and power and in fuel-cell-poweredvehicles. In fuel-cell-powered vehicles, frequent start-ups may occurresulting in exposure of the partial oxidation catalyst to thermalshocks. Since the process and reactor according to the invention isparticularly suitably under thermal shock conditions, the fuel cellsystem according to the invention can advantageously be applied infuel-cell-powered vehicles.

[0044] Accordingly, the invention further relates to a vehicle providedwith a fuel cell system as hereinbefore defined.

[0045] The invention will now be illustrated by means of schematic FIGS.1 to 3.

[0046]FIG. 1 shows a side view of a longitudinal section of oneembodiment of a catalyst system that can suitably be used in the processaccording to the invention.

[0047]FIG. 2 shows a longitudinal section of a part of a reactorcontaining the catalyst system of FIG. 1.

[0048]FIG. 3 shows a longitudinal section of a part of anotherembodiment of a reactor that can suitably be used in the processaccording to the invention.

[0049] The catalyst system 1 shown in FIG. 1 comprises a hollowcylindrical downstream part 2 and an upstream part 3. The downstreampart 2 is in the form of a porous arrangement of catalyst carrier in theform of metal fibres (fecralloy-type fibres) knitted and pressed in theshape of a hollow cylinder and provided with Rh and Ir as catalyticallyactive metals and Zr as modifying cation. The upstream part 3 comprisesa resilient fecralloy-type metal foil as catalyst carrier that isprovided with Rh and Ir as catalytically active metals and Zr asmodifying cation. The upstream part 3 is bend in the form of a ring thatis arranged on part of the upstream surface 4 of the downstream part 3.

[0050] In FIG. 2 is shown part of a reactor containing the catalystsystem of FIG. 1, i.e. the downstream part 2 and the upstream part 3arranged on part of its upstream surface 4. The upstream part 3 iscontained in the upstream part 5 of the reactor and the downstream part2 is contained in the downstream part 6 of the reactor. The reactorfurther comprises a first reactant supply conduit 7 for supply ofhydrocarbonaceous feedstock and a second reactant supply conduit 8 forsupply of molecular-oxygen containing gas and, optionally, steam. Duringnormal operation of the reactor, the reactants supplied via conduits 7and 8 are mixed in a mixing zone 9, wherein a swirling movement isimposed on the thus-formed feed mixture. The swirling flow 10 of feedmixture is contacted with the catalyst system 2, 3. Part of the feedmixture is converted at the upstream part 3 of the catalyst system andpart will be converted at the downstream part 2. Effluent is dischargedvia effluent discharge chamber 11 and discharge conduit 12. The overalldirection of the fluid flow in the upstream part 5 of the reactor is indictated with arrow 13. In the downstream part 6 of the reactor, theoverall direction of the fluid flow is indicated with arrow 14.

[0051] In FIG. 3 is shown part of a reactor tube 15 having an upstreampart 5 and a downstream part 6. The reactor contains a catalyst systemhaving an upstream part 2 in the form of a round, metal catalyst carrierplate provided with Rh and Ir as catalytically active metals and Zr asmodifying cation, and a downstream part 3 in the form of metal fibres(fecralloy-type fibres) knitted and pressed in the shape of a cylinderand provided with Rh and Ir as catalytically active metals and Zr asmodifying cation.

[0052] During normal operation of the reactor, a flow of feed mixture 18is first contacted with the metal plate 3 and then with the downstreampart 2 of the catalyst system. Effluent is discharged in the directionindicated by arrow 19.

[0053] The diameter of the metal plate 3 is smaller than the innerdiameter of the reactor tube 15 such it only partly fills thecross-sectional area of the fluid flow path and (partly converted) feedmixture can pass the pre-conversion structure in order to be able tocontact the upstream surface 4 of the downstream part 2 of the catalystsystem.

[0054] The process according to the invention will be furtherillustrated by means of the following examples.

EXAMPLES Example 1 (According to the Invention)

[0055] Catalyst System

[0056] Downstream Part

[0057] A catalyst carrier in the form of a knitted arrangement ofcommercially available fecralloy wire (wire diameter 0.2 mm; ex.Resistalloy, UK; wire composition: 72.6% wt Fe, 22% wt Cr, 5.3% wt Al,and 0.1% wt Y), pressed in the shape of a hollow cylinder (outerdiameter: 63 mm; inner diameter: 20 mm; height: 32 mm) was calcined at atemperature of 1050° C. during 48 hours. The calcined wire arrangementwas once dipcoated in a commercially available partially-stabilisedzirconia (zirconium oxide, type ZO, ex. ZYP Coatings Inc., Oak Ridge,USA). The zirconia is partially stabilised with 4% wt CaO. Afterdipcoating, the arrangement was calcined for 2 hours at 700° C.

[0058] The coated arrangement was further provided with 0.7% wt Rh, 0.7%wt Ir, and 2.0% wt Zr, based on the total weight of the downstream part,by immersing it three times in an aqueous solution comprising rhodiumtrichloride, iridium tetra chloride and zirconyl nitrate. After eachimmersion, the arrangement was dried at 140° C. and calcined for 2 hoursat 700° C.

[0059] Upstream Part

[0060] A commercially available resilient foil of PM 2000 (ex. PLANSEE,Austria; foil composition: 23.5% wt Fe, 20% wt Cr, 5.5% wt Al, 0.5% wtTi, and 0.5% wt Y) having a length of 60 mm, a height of 15 mm, and athickness of 0.125 mm was calcined at a temperature of 1050° C. during48 hours. The calcined foil was once dipcoated in the samepartially-stabilised zirconia as applied for the downstream part (seeabove). After dipcoating, the foil was calcined for 2 hours at 700° C.The coated foil was further provided with 1.0% wt Rh, 1.0% wt Ir, and2.8% wt Zr, based on the total weight of the coated foil, by immersingit twice in an aqueous solution comprising rhodium trichloride, iridiumtetra chloride and zirconyl nitrate. After each immersion, the foil wasdried at 140° C. and calcined for 2 hours at 700° C.

[0061] Catalyst System

[0062] The resilient foil 3 is inserted at the inside of the cylindricaldownstream part 2 to form a ring, as shown in FIG. 1, such that part ofthe formed ring covers part of the upstream surface 4, i.e. the surface4 at the inside of the cylinder forming the downstream part 2. The ringis arranged against the upstream surface 4 over a height of 5 mm.

[0063] Catalytic Partial Oxidation

[0064] The catalyst system as described above is placed in a reactor asshown in FIG. 2. Naphtha (0.74 g/s), air (3.45 g/s), and steam (0.85g/s) were mixed, pre-heated to a temperature of 190° C. and brought intoa swirl movement. The swirling, pre-heated feed mixture was contactedwith the catalyst system as shown in FIG. 2. The temperature of theupstream surface of the cylinder and the temperature of the ring weremeasured by means of an optical pyrometer.

[0065] Temperature of the upstream surface of the cylinder (downstreampart of the catalyst system): 1060° C. Temperature of the ring (upstreampart of the catalyst system): 1180° C.

Example 2 (Not According to the Invention)

[0066] A catalyst system in the form of a hollow cylinder was preparedin the same way as the downstream part of the catalyst system describedin Example 1. The thus-prepared catalyst comprised 0.7% wt Rh, 0.7% wtIr, and 1.9% wt Zr, based on the total weight of the catalyst. Thecatalyst was placed in a reactor similar to that shown in FIG. 2, butwithout an upstream part 3. A catalytic partial oxidation process wasperformed under the same conditions as described in Example 1.

[0067] Temperature of the upstream surface of the catalyst: 1175° C.

1. A process for the catalytic partial oxidation of a hydrocarbonaceousfeedstock, wherein a feed mixture comprising the hydrocarbonaceousfeedstock and a molecular-oxygen containing gas is contacted with acatalyst system having an upstream part and a downstream part, thedownstream part being in the form of a porous catalyst bed, wherein thecatalyst system is retained in a reactor, the reactor comprising anupstream part that contains the upstream part of the catalyst system anda downstream part that contains the downstream part of the catalystsystem, wherein the upstream part of the catalyst system only partlyfills the cross-sectional area of the fluid flow path of the upstreampart of the reactor and the downstream part of the catalyst systemcompletely fills the cross-sectional area of the fluid flow path of thedownstream part of the reactor.
 2. A process according to claim 1,wherein 5 to 75% (v/v) of the feedstock is converted at the upstreampart of the catalyst system, preferably 10 to 50% (v/v), more preferably15 to 40% (v/v).
 3. A process according to claim 1 or 2, wherein thetemperature of the upstream surface of the downstream part of thecatalyst system is at most 1150° C., preferably at most 1100° C.
 4. Aprocess according to any one of the preceding claims, wherein the feedmixture has a swirling movement when contacting the downstream part ofcatalyst system.
 5. A process according to any one of the precedingclaims, wherein the upstream part of the catalyst system is in the formof a metal catalyst carrier provided with a catalytically activematerial.
 6. A process according to claim 5, wherein the metal is ahigh-temperature resistant metal, preferably an alloy comprising iron,chromium and aluminium, more preferably a fecralloy-type alloy.
 7. Aprocess according to claim 5 or 6, wherein the metal catalyst carrier ofthe upstream part of the catalyst system is in the form of a non-porousmetal structure, preferably a metal plate or foil.
 8. A processaccording to any one of claims 5 to 7, wherein the upstream part of thecatalyst system is provided with means for electrically heating it.
 9. Aprocess according to any one of the preceding claims, wherein thecatalyst bed of the downstream part of the catalyst system comprises ametal catalyst carrier provided with a catalytically active material.10. A process according to claim 9, wherein the metal catalyst carrierof the catalyst bed of the downstream part of the catalyst system is anarrangement of metal wire, preferably a knitted arrangement of metalwire.
 11. A process according to any one of the preceding claims,wherein the upstream part of the catalyst system is arranged on part ofthe upstream surface of the downstream part of the catalyst system. 12.A process according to any one of the preceding claims, wherein theupstream part of the catalyst system is provided with means fordetermining its temperature.
 13. A reactor comprising a catalyticreaction zone comprising the catalyst system as described in any one ofclaims 1 and 5 to 12, the reactor further comprising a catalyticreaction zone for the water-gas shift conversion of the effluent of thedownstream part of the catalyst system.
 14. A fuel cell systemcomprising the reactor according to claim 13 and a fuel cell. 15.Vehicle provided with a fuel cell system according to claim 14.